In the wireless communication field, in order to improve system performance and meet the continuously increasing data service requirements of users, Orthogonal Frequency Division Multiplexing (abbreviated as OFDM) and Multiple-Input Multiple-Output (abbreviated as MIMO) are introduced.
During transmission, in order to further improve transmission quality, the data flow and pilot after MIMO encoding can be pre-coded and then mapped onto different antennae for transmitting. Thus, dedicated pilot appears. In an MIMO system which uses dedicated pilot mode, what is obtained by using channel estimation is an equivalent channel after pre-coding, and as to a system which needs to feed back real channel condition, the equivalent channel has to be converted to the real channel, while the process of converting the equivalent channel to the real channel is complicated and even cannot be achieved; in addition, as to a terminal which does not transmit any data, during a time period, it cannot obtain the real channel situation periodically. For this end, it needs to measure the current real channel condition to meet the requirements of system feedback.
Middle pilot sequence refers to inserting a specific pilot sequence on a specific OFDM symbol (FIG. 1) in a downlink wireless resource frame, and it is different from ordinary dedicated pilot and is not pre-coding processed so that the receiver carries out channel measurement. The middle pilot can be used to estimate the channels of all carrier locations on the entire symbol, so that it is convenient for the transmitter to rationally use highly efficient transmission strategy according to the current channel condition. In a wireless communication system, rationally using middle pilot to measure real channel condition, correctly feeding back channel quality information (abbreviated as CQI), pre-coding matrix index (abbreviated as PMI) and rank indication (abbreviated as RI) of the channel are very important for improving the transmission efficiency of the system.
Since the orthogonal frequency division system is a multi-carrier system, different sequences of frequency domain modulation will affect the maximum peak-to-average power ratio (PAPR) of its time domain symbol, thus affecting the efficiency of system power amplifier; if the PAPR corresponding to the modulated middle pilot is too big, it would cause the transmitter to carry out non-linear processing, thus affecting the channel estimation accuracy of the receiver, which will finally affect the downlink performance of the users. On the other hand, since the middle pilot sequence is sent through the same OFDM symbol of the same subframe of a plurality of adjacent cells, the interference maybe exist therebetween, which makes the terminal to receive middle pilot signals of the serving base station and adjacent base station simultaneously. As to any rational design and rationally sending the middle pilot sequence, there is still no effective solution currently.
During the implementation of the present invention, the inventors recognized that there are the following defects in the prior art: during the process of sending middle pilot, the pilot symbol has periodicity in the frequency domain, thus affecting the downlink performance of user data.